-- Discussion containing changed information from previous version are highlighted. --
525
FXUS62 KRAH 181821
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
220 PM EDT Sat May 18 2024

.SYNOPSIS...
The region will remain in a warm, humid, and unsettled weather
pattern through tomorrow. Cool high pressure will build in from
the north tomorrow afternoon through Monday, then shift off the Mid
Atlantic coast late Monday.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 1145 AM Saturday...

Water vapor imagery depicts a shortwave over western TN and northern
MS and mid/upper ridging over the western Atlantic, with central NC
under the influence of southwesterly flow in between these two
features. This is helping bring deep Gulf moisture into the area
with PW values ranging from 1.3 to 1.6 inches, and they will reach
as high as 1.75 to 2 inches (or over 150% of normal) later today. A
plume of convection extends NE from the central Gulf Coast to the FL
panhandle, southern GA and eastern SC, along and north of a stalled
boundary. The northern extent of that convection may affect our far
southern counties late this morning and early this afternoon, and it
is already exhibiting a small amount of lightning. Elsewhere across
central NC, mainly dry conditions are expected until after 18z when
showers and storms will start popping up. The focus of this
convection will likely be a boundary that is currently analyzed over
our far northern counties close to the VA border, separating S winds
and dew points in the upper-60s to lower-70s from E winds and dew
points in the upper-50s to lower-60s.

The CAMS have been consistently showing a W-E oriented line of
showers and storms developing along this boundary that sinks south
this afternoon and evening as the front sinks south, clearing our
area by around 06z. So went with categorical POPs with this line,
and the rain could be heavy at times. 12z HREF PMM totals depict
potential for 1.5 to 2 inches in localized spots. There were
localized spots in the NE Piedmont that received 2+ inches of rain
in the last 24 hours, particularly around northern Durham/Orange and
southern Granville counties. However, these totals were isolated
enough and the high totals today are expected to be isolated enough
to prevent widespread flash flooding. Even still, isolated flash
flooding is certainly possible and the WPC has all of central NC in
a marginal (level 1 of 5) risk for excessive rain. The line will
clear our CWA by around 06z, but isolated showers will still be
possible overnight as the shortwave approaches from the west.

As for the severe threat, SPC also has all of central NC in a
marginal risk for severe storms, with a primary threat of damaging
winds. Not expecting a tornado threat given the very weak 0-1 km
shear of around 5 kts or less. The 0-6 km shear is better but still
marginal for severe weather, around 30-35 kts. Instability will also
be limited somewhat by the widespread cloud cover in place across
the area, but the 12z HREF still shows as much as 1000-1500 J/kg of
SBCAPE by late this afternoon. The greatest instability will be
across our south, while our far northern counties to the north of
the boundary will be mostly stable and the severe threat looks much
lower there.

High temperatures today will range from lower-to-mid-70s in the far
NE to near 80 in the far south. Lows tonight will be upper-50s to
mid-60s.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
As of 220 PM Saturday...

By Sunday morning, surface low pressure should be off the NC/SC
coast with a positively tilted upper trough axis extending across
the Delmarva Peninsula through North Carolina into northern Georgia.
Both the surface low and the upper trough will move east through the
daytime, with the trough axis near the Atlantic coastline by the
evening. High-resolution and synoptic models have continued the
trend from the last couple days of showing drier conditions overall.
It now appears that locations north of US-64 should be dry through
the day, with a slight chance of showers to the south of that and a
chance of thunderstorms along the southernmost border. Any
precipitation should come to an end by the evening, with dry
conditions overnight. The upper trough will help to keep conditions
mostly cloudy through the morning, then at least some partial
clearing will occur during the afternoon. Northeasterly flow should
occur through the day, becoming lighter overnight, but the cold
advection on the backside of the surface low should make Sunday the
coolest day out of the next seven. Some locations across the
northeast should remain in the upper 60s, but otherwise highs will
be in the lower 70s.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 134 PM Saturday...

Monday through Wednesday: Aloft, the trough should be offshore, with
the sub-tropical ridge building from the southern plains to the
Northeast US early Mon. While the trough should linger off the mid-
Atlantic coast through Wed night, the ridge will shift slightly
sewd, extending from the lower MS Valley to the mid-Atlantic by 12Z
Wed. The ridge axis will generally remain over the area through at
least Wed night, albeit continuing to drift sewd. At the surface,
the ridge will remain in place through Mon night, while the low
sits/drifts eastward offshore. The surface high will settle south
over the mid-Atlantic coast through Tue before drifting eastward
over the Atlantic, but continuing to ridge westward toward/into the
area, on Wed. A warm front may lift northward through the area Wed
as the high moves away, with a lee trough strengthening over the
area Wed night. While Mon should be largely dry, there is still the
possibility for a brief period of lingering light rain early.
Otherwise, the forecast through Wed night is currently dry. As for
temperatures, there some continued uncertainty in highs on Mon, but
for now expect low/mid 70s east to upper 70s west. Lows should
generally be in the low to mid 50s Mon night. Expect temperatures to
moderate through mid-week.

Thursday onward: A northern stream low will track enewd through the
western Great Lakes and into Ontario Canada Wed/Thu. The ridge will
be suppressed sewd Thu/Fri as a s/w tracks from the mid-MS Valley,
enewd into the northern mid-Atlantic/Northeast US. This wave may
briefly amplify the larger scale trough over the Northeast and mid-
Atlantic Thu night/Fri. There is the potential for showers/storms
across the area with this disturbance Thu/Thu night. Meanwhile,
another s/w will move through the southern/central Plains Thu,
through the mid-MS Valley Thu night/Fri, then enewd through the
Appalachians Fri/Fri night. There are still some timing/location
difference between the medium-range model solutions, so those
details remain unclear. However, there will be another chance for
showers/storms with this system if/when it track through the mid-
Atlantic/Carolinas Fri/Sat. Expect continued near to above normal
temperatures through Sat.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 200 PM Saturday...

Mostly VFR conditions are now being observed across central NC, but
several sites are still reporting MVFR ceilings. The region is
mostly precipitation free, but a few showers and storms are
beginning to pop up in the south around FAY and across the north.
The northern line will strengthen and become the main focus for poor
aviation conditions from later this afternoon into this evening as
it sinks south through the area. Heavy rain, gusty winds, MVFR
ceilings and IFR visibilities will be possible with these storms.
Behind the line, a few showers may linger into the overnight hours
especially across the east. Ceilings will also drop to IFR
everywhere, with periods of LIFR ceilings not out of the question.
Ceilings will slowly improve to MVFR by late morning and early
afternoon tomorrow. Winds will shift from SW to NE this afternoon
and evening, remaining NE around 5-10 kts from the overnight hours
into the day tomorrow.

Outlook: Some moisture will linger during the day Sunday with at
least MVFR cigs possible Sunday night. A return to dry weather and
VFR is more plausible from Monday onward. The next cold front will
bring a chance of showers and storms on Thursday.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Hartfield/Leins
NEAR TERM...Danco
SHORT TERM...Green
LONG TERM...KC
AVIATION...Danco/Leins